linux-kernel - Re: [PATCH v4 2/3] PCI: dwc: ep: Add per-PF BAR and inbound ATU mapping support

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Message-ID: <b2dfa96a-4b8f-4927-bad7-23cb1e2c6483@ti.com>
Date: Fri, 30 Jan 2026 16:22:57 +0530
From: Aksh Garg <a-garg7@...com>
To: Niklas Cassel <cassel@...nel.org>
CC: Koichiro Den <den@...inux.co.jp>, <linux-pci@...r.kernel.org>,
	<jingoohan1@...il.com>, <mani@...nel.org>, <lpieralisi@...nel.org>,
	<kwilczynski@...nel.org>, <robh@...nel.org>, <bhelgaas@...gle.com>,
	<Zhiqiang.Hou@....com>, <gustavo.pimentel@...opsys.com>,
	<linux-kernel@...r.kernel.org>, <s-vadapalli@...com>, <danishanwar@...com>
Subject: Re: [PATCH v4 2/3] PCI: dwc: ep: Add per-PF BAR and inbound ATU
 mapping support



On 30/01/26 16:17, Niklas Cassel wrote:
> On Fri, Jan 30, 2026 at 04:09:26PM +0530, Aksh Garg wrote:
>> On 30/01/26 15:23, Niklas Cassel wrote:
>> > On Fri, Jan 30, 2026 at 09:42:43AM +0530, Aksh Garg wrote:
>> > > On 29/01/26 19:44, Niklas Cassel wrote:
>> > > > On Thu, Jan 29, 2026 at 02:47:52PM +0530, Aksh Garg wrote:
>> > > > > -static void dw_pcie_ep_clear_ib_maps(struct dw_pcie_ep *ep, enum pci_barno bar)
>> > > > > +static void dw_pcie_ep_clear_ib_maps(struct dw_pcie_ep *ep, u8 func_no, enum pci_barno bar)
>> > > > >  {
>> > > > > +	struct dw_pcie_ep_func *ep_func = dw_pcie_ep_get_func_from_ep(ep, func_no);
>> > > > >  	struct dw_pcie *pci = to_dw_pcie_from_ep(ep);
>> > > > >  	struct device *dev = pci->dev;
>> > > > >  	unsigned int i, num;
>> > > > > @@ -152,18 +157,18 @@ static void dw_pcie_ep_clear_ib_maps(struct dw_pcie_ep *ep, enum pci_barno bar)
>> > > > >  	u32 *indexes;
>> > > > > Hello Aksh,
>> > > > > Considering that all other functions that you have modified, you
>> > > have added a:
>> > > > > if (!ep_func)
>> > > > 	return;
>> > > > > > I think you should do the same to this function.
>> > > >
>> > > 
>> > > I omitted this NULL check here because all the current call sites of
>> > > dw_pcie_ep_clear_ib_maps() already perform this validation. I felt
>> > > adding it here would add redundancy in the code.
>> > 
>> > Ok, but with that logic, shouldn't we also remove the NULL checks from
>> > dw_pcie_ep_ib_atu_bar() and dw_pcie_ep_ib_atu_addr(), because they are
>> > only called from dw_pcie_ep_set_bar(), which already has the ep_func
>> > NULL check?
>> > 
>> 
>> Yes, that's correct. Alternatively, we can add the NULL check in
>> dw_pcie_ep_clear_ib_maps() as well, making all the functions using
>> ep_func self-contained and defensive, removing the dependency on whether
>> the callers perform NULL checks. This makes the code more future proof,
>> as new callers won't need to be aware of the NULL pointer possibility.
> 
> Sounds like a good idea to me.
> 
> Neither of these functions is in the hot path, so the performance of having
> one less NULL check is not super critical.
> 

Okay, I will post a new patch series adding the NULL check in the
function.

Regards,
Aksh Garg

> 
> Kind regards,
> Niklas
>